diff --git a/py/test/rsession/slave.py b/py/test/rsession/slave.py
index 0c13743e7..d9b17c3d4 100644
--- a/py/test/rsession/slave.py
+++ b/py/test/rsession/slave.py
@@ -133,6 +133,7 @@ def setup():
     sys.path.insert(0, basedir)
     import py
     config = py.test.config
+    config.option.boxed = True
     assert not config._initialized 
     config.initdirect(basedir, config_repr)
     if not config.option.nomagic: